1. Deterioration of reagents
Occasionally difficulties in ABO grouping are caused by using expired or contaminated reagents or incorrectly prepared or heavily contaminated
physiological saline.
Correction: Appropriate controls should be used to check the reactions of antisera and test cells.
Prepare fresh saline if contamination is suspected (check a sample microscopically).
2. Rouleaux
Rouleaux causes red cells to stack together (like piles of coins), giving the appearance of agglutination when there is no true agglutination. It can occur when
a patient has a protein abnormality, e.g. myelomatosis or when dextran, PVP, or similar product has been given intravenously. In cord blood samples, rouleaux can be caused by contamination
of the sample with gel substances such as Wharton’s jelly when applied to the cord of a newborn (wash the infant’s red cells with saline).
Marked rouleaux can cause discrepancies in serum grouping (particularly when tile grouping) and occasionally in cell grouping when using whole blood, unwashed or insufficient washed red cells.
Rouleaux can usually be distinguished from true agglutination by examining the red cells microscopically.
Correction: Whenever suspected, add a drop of saline to the cells. Rouleaux usually disperses after 1–2 minutes following the addition of saline. Serum grouping should be repeated using serum diluted 1 in 2 in saline (mix 1 drop of saline with 1 drop of serum).
This will cause rouleaux to disperse
3. Autoagglutinins
Occasionally a patient’s serum may contain autoagglutinins which are antibodies that cause the agglutination of a person’s own and other red cells (autoagglutination). They are known to occur in lymphoma, leukaemia, virus pneumonia, systemic
lupus erythematosus and other autoimmune diseases, and occasionally in severe falciparum malaria. Autoagglutination may also occur following
treatment with some herbal preparations. Cold agglutinins active at room temperature are a frequent cause of autoagglutination.
When autoagglutinins are present, a patient’s red cells appear agglutinated before commencing grouping. This can be confirmed by setting up an autocontrol.
Correction: When autoagglutination due to cold agglutinins is suspected, the cell grouping should be repeated after washing the patient’s red cells in warm saline and the serum group and autocontrol
read after incubation at 37°C. The autocontrol should then be negative.
4. Faulty technique
When it is possible that a technical error in blood grouping has occurred, repeat the cell and serum grouping (using a spun tube technique).
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